创建从现有对象继承的新对象时的三点JavaScript问题

function Parent() {
  this.name = 'Parent';
}

Parent.prototype.sayHello = function() {
  console.log('Hello, ' + this.name);
};

function Child() {}

Child.prototype = new Parent(); // 子类的原型设置为父类的实例

var child1 = new Child();
child1.name = 'Child1';
child1.sayHello(); // 输出: Hello, Child1

var child2 = new Child();
child2.sayHello(); // 输出: Hello, Child1，因为name属性被共享了

function Child() {}

Child.prototype = Object.create(Parent.prototype);
Child.prototype.constructor = Child;

var child1 = new Child();
child1.name = 'Child1';
child1.sayHello(); // 输出: Hello, Child1

var child2 = new Child();
child2.sayHello(); // 输出: Hello, undefined，避免了属性共享的问题

function Parent(name) {
  this.name = name;
}

Parent.prototype.sayHello = function() {
  console.log('Hello, ' + this.name);
};

function Child(name) {
  Parent.call(this, name); // 调用父类构造函数
}

var child = new Child('Child1');
console.log(child.name); // 输出: Child1
child.sayHello(); // 报错: child.sayHello is not a function

function Child(name) {
  Parent.call(this, name); // 调用父类构造函数继承实例属性
}

Child.prototype = Object.create(Parent.prototype);
Child.prototype.constructor = Child;

var child = new Child('Child1');
console.log(child.name); // 输出: Child1
child.sayHello(); // 输出: Hello, Child1

class Parent {
  constructor(name) {
    this.name = name;
  }

  sayHello() {
    console.log('Hello, ' + this.name);
  }
}

class Child extends Parent {
  constructor(name) {
    super(name);
  }

  greet() {
    setTimeout(function() {
      this.sayHello(); // 这里的this指向全局对象，导致错误
    }, 1000);
  }
}

var child = new Child('Child1');
child.greet(); // 报错: this.sayHello is not a function

class Child extends Parent {
  constructor(name) {
    super(name);
  }

  greet() {
    setTimeout(() => {
      this.sayHello(); // 箭头函数自动绑定this
    }, 1000);
  }
}

var child = new Child('Child1');
child.greet(); // 输出: Hello, Child1